To overcome the shortcomings of prior art etching chambers, a new method and apparatus for etching semiconductor devices is provided.
Plasma dry etch reactors are vacuum chambers in which an electrical plasma is created in order to etch semiconductor wafers. The etching is usually performed through a photoresist mask.
Dry etching techniques are often referred to as reactive ion etching or plasma etching. Prior art dry etchers form a plasma by injecting precursor gases into an area where a RF Field is produced. The precursor gases may include fluorine containing gases, for example, CHF.sub.3 or CF.sub.4.
The RF field can be generated by two or three internal electrodes coupled to a RF source, or by means of external electrodes or a coil. The high frequency excitation causes the precursor gases to change into the plasma which generates ions and reactive species. The reactive species created diffuse to the surfaces to be etched where the etching is chemical. In ion-assisted processes, the semiconductor devices are exposed to the energetic ions of the plasma. The ions are directed at the semiconductor device where the ions then collide with the substrates causing portions of the surface of the substrate to etch, or chip, off. The ion-assisted etching processes involve both chemical and physical etching.
During the etching process, fluorocarbon films are deposited onto the walls of the etching chamber. The deposition of the fluorocarbon films changes the impedance of the system and over time results in a decrease of the self-biasing voltage of the etching chamber. This changes the operational characteristics of the etcher affecting the etching process. Additionally, the fluorocarbon film deposited on the walls of the etching chamber may flake off and become a source of particles within the etching chamber.
The deposition of fluorocarbon films on the etching chamber walls is conventionally dealt with by cleaning the etching chamber using an O.sub.2 plasma and subsequently reconditioning the etching chamber. The chamber cleaning and seasoning process can require up to 30 percent of the total system up-time.
Some prior art designs have provided methods and/or apparatuses in an attempt to eliminate some of the problems caused by the deposition of the fluorocarbon films onto the surfaces within the etching chamber. For example, in one system a substrate to be etched is placed within the etching chamber and cooled while the walls of the chamber are heated to a temperature of approximately 80 C. Heating of the surfaces is accomplished by supplying hot water to a pipe mounted on the outer surfaces of the dry etching device. This is done to reduce bonding of a polymer film to the walls of the etching device while the substrate is being etched.
However, this method and/or apparatus will only reduce the deposition rate of the fluorocarbon films on the inner walls of the chamber marginally. Furthermore, where high-density plasma tools are employed during the etching process, a partial elimination of the deposition rate of, for example, 10 to 20 percent by heating to 80 C, will still result in a high frequency of cleaning for the etching chamber.